Method and apparatus for forming fibers



y 1952 c. J. STALEGO ET AL 3,

I METHOD AND APPARATUS FOR FORMING FIBERS Filed Dec. 30, 1948 2 SHEETS-SHEET 1 INVENTOR- C'ka'nlmt 16101890 1 Warren HDr m am:

y 1952 c. J. STALEGO ET A| 2,603,833

" METHOD ANb APPARATUS FOR FORMING FIBERS Filed Dec. 30, 1948 I 2 SHEETS--SHEET 2 IETi-E 1N VEN TOR. (harried J 512102 0 1 War/h Nflrummemd A F TOE/3155K S Patented July 22, 1952 ohe les J QStalego' and Wendell mum-mend, Newark, Ohio, 'assignors ""'to"0wens Cornin'g'-" Fiberglas Corporation ration of Delaware Application December 30, 1948, Serial 58,164

. 1 This invention relates to an improved method and apparatus for producing fibers from glass or materials which become molten or soft when subjected to heat and which may be drawn out into finefibers when in a softened state. I I

: One of the objects of this invention is to provide a simple and economical process and apparatus for producing fibers which may be as fine as one, micron or less in diameter from a body of heat softened glass ormaterial having characteristics similar to glass. H

..Another object of this invention is to subject a body of-,heat, softened material to the action of centrifugal force of suificient magnitude to draw out the material and project the same into a blast :of gas moving at a velocity high enough to further drawout the material into fine fibers. In accordance with this invention the blast .is obtained by burning a combustible mixture of gases within a combustion chamber at pressures above atmospheric and by discharging the burned gases or products of combustion from the chamher through an outletso proportioned with r spect to-the quantity of gas burned in the chamberthat-the burned gases are forced from the chamber at a velocitysuflicient to attenuate heat softenedglass into fibers, 1

;.Still another objectof this invention is to heat the material or g-lassto a temperature abovethe softening point thereof; by introducing the material directly into the burner combustion chamber duringthe interval the combustible mixture of gases is burning within the chamberand thereby eliminating the necessity of providing separate burners or heating devices for heating the material to the softening or attenuating temperature.

Afurther object of this invention is to rotate the bottom wall of the chamber on which the heat softened material collects at a speed determined to provide the centrifugal force required the burner outletandare attenuated into fine flbersbyv theforce of the blast.

Stillanother' feature of this invention is to heat the" glass to such a high-temperature within the burner that the glass issuing from the burnerjis in a very high fluid condition and is atomized or broken up into extremely'fineparticles by the action of centrifugal forcefland the blast of burned gasesfand these'partic'le'sare then'atten uated into fineffibers as theyc'ool in 'their'jhigh sectional view tnrou n'eneftype of apparatus capable' of carryingout the several steps of'the process; I Fig-ureZ is a cross-sectional viewtaken'onthe lin 2 of Figure 1; k' Figure'B is a cross-sectional view taken on the line'3--3of'Figure'1"; Figure 4 is a semi-diagrammatic longitudinal sectional view of a modified form of apparatus; and I x t Figure 5 is'a diagrammatic sectional view similar to Figure 4 showing still another embodiment of this invention. t .It will be vapparent as this description proceeds thatithe process and" apparatus disclosed herein may be successfully employed to produce fibers on a commercialbasisfrom inorganic materials other than glass but "having characteristics "siniilar memes; Such materials are of a nature which'become softivhen subjected to heat and are capable of'bein'g 'diawnoutinto fine fibers Whenin a softened condition. These properties are present in' many different'types of thermoplastic materials. and are 'also' found'in various kinds of synthetic resins. However, the present invention has been particularly developed'in con neotion with the manufacture of glass fibers and for this reason glass is referred to particularly invthe following description;

vThe various "steps'of' the process will perhaps be morerun understood by a description of one type of apparatus that may be employed for carryingl outthefs'teps of the process. With this in view, reference is made to the embodiment of the invention shown in Figures 1 to 3 inclusive of the drawings. In detail, the numeral l0 indicates a cylindrical barrier having refractory side and end walls H and I2 respectively. The burner ID is suitably s'uppprted'in a vertical position and the end wall I2 forms the bottom of the burner. The refractory walls of the burner are enclosed in 'a' suitable metal casingl3 and the ilatteris Journaled in bearings l 4 carried by suitable sup-.-

porting structure l5 in a manner to enable rotatop wall 11 and rotates as ajunit with the l0. Cooperating with the top to form a fuel mixture inlet 2| formed of a refractory material and secured in the burner at the top of the combustion chamber It. The opening through the ring is of a 4 H mixture burned within the combustion chamber [6 that the burned gases are forced through the slots 28 in the form of a blast having a temperature which exceeds the softening temperature of diameter to receive the lower end of the supply tube I9 and the latter is suitably secured to the rin a st v u l m xture s i it ci u v atte cl'iamber- 20 through a plurality of ports 22 formed iii th" sidewall of the burner adjacentthe top of atter and spaced equal distances from each other ircumferentially of the burner v r The parts 22 communicate with an annular 'manifold 23 fixedjtothe support l5 and connecte'd to asource or fuel mixture bye conduit 24; It rouowsrrom the'above thatthe burner l0 rotates relativeto t e-1 fs l 'nly m if ld 2 a inmo d spreven the escape of 'fii'elmixture from the a'n'ifold suitable sealing means is provided between the adjacent surfaces of the manifold and burner. One type of seal that may be used for the abbve purpose is shown in Figure er the drawings as comprising a pair of contracting "sealing fin'gs25 respectively supported in annulargrooves 26.formed in the inner surface o'f the annular manifold 'at oppo'site jside's [of .the' fuel supply chamber therein. These'rings respectively frictionally engage the metal casing l3 at opposite s des... bf he or 2 nd thereby prev t the escape of fuel mixture flowing from the manifold 23.t.o th P rtsZZ-J r v. r H

fufe m x u .em h ema.b ord y ra -ga or manufactured gas mixedwith the 'erfal guntfofa r by ortho o mi n eq ipjii t Show h l ilf. I fanyfc 's the mle inixture Ofga'ses i introduced into the bu er at pressures somewhat above atmospheric P fit pa 'ation f the mi ure. nthe at s re,

, "I'h'ecombusti blemixture of gase's are admitted .tcth'e jcombustiojn'chambfer l6 through a multip city o f passages 21 formed in the ring 2| and a igniteu as they enter the chamber I6 The Z: mbustible jmixture of i'gasesburnjwithin the ,of the chamber [6 toieffectayery high rate of expansion and the resulting temperature heats t e r a to iw s o tha me t to "De hi. i'rl j t hei Walls. t eeom mQa dSs enF- "ek r m lyn 'h mperaturecithegrer tq wan o'f. the chamber [6 ,accelerates'th e rateof bu ningfof' the combustiblemixtur I f gasesjsubls'tantially above ,the'rate ofv flame propagationof heses ix fire'in t e e mo phere. i,

bur ea e or Pro c s f mhus'tic r discharged from the combustion chamber "[6 ,thro hanl ality joffsl ts :zarormedin'the s de 'll jl l 'of the burnerat ;theb,ottomofthejcham ibr115e dfs a ed ,e fardistance from'eachothfer girc fi re a v t e i 'u' 'nj -...'T f ,.'Qmbinefd traf r e e g u t even. 8 16 site w petitioned with respect to "thetuantity'tr'mn re and ata rate belo'w the rate fofjflame the rate of name propagation of the combustible mixture of gases in the atmosphere and provide ample force to reduce a body of glass of substantial size to fibers having diameters as small as one micron or less.

It will of course be understood that the combined area of the outlet openings 28 may be varied to some extent'relative to the volume or the combustion chamber I (i, depending upon the heat required in the blastissuing from the outlet openings. Outlet openings providingagreat'ei' area relative to the volume 'of the cbmbustion chamber It permit burning a greater amountof gas and result in generating higher heat in the blast. However, this advantage is obtained "at the expense of the Velocity of the blast and for this reason the Y combined area of the outlet openings 28 ordinarily no greater than necessary to obtain in the blast the heat required "to raise or maintain [the temperature of theglass to the desired attenuating temperature.

In accordance with the present invention the Heat resulting from the high rate of combustion withinthe chamber [6 is employed to 'melt or sdft'en a body'of glass'prior to'reducing the latter to line fibers. 7 As shown particularly in Figure '1 of the drawings, glass is supplied into the com-'- biistidn chamber l6 through the tube l9 from"a tank or receptacle '29 diagrammatically 'showna's having an entrant conduitl30 and a discharge opening 3|. The discharge opening 3| is formed in the bottom of the tank '29 and the latter is supported so that the opening 3| registers with the upper end of the supply tube I9. In the present instance the combustible mixture bi. gassjis introducd into the tank '29 through the opening 30 and is burned in the space provided in the "tank abov the level or the mass. The cbinbustible mixture of gases supplied'to'the tank 25n'iay bethe same as the-gas admitted to the 'burner'ifl and is preferably burned inthe ta'nkj29 to provide a pressure on the'gla'ss 'whichissufficiently high to enable feeding the glassintb" the burner against the pres'sure'existin'g in the oombustipncliamber l6.

v follows from the above that the supply-or glass is heated inthetanl; 29 efore bein'gfi'ntrofiuced into the combustion chamber I6. This initial heating of the rass within the tank-29 1s not required, however, because the temperature available within the combustion chamber l e-is e id ne. an tr me 'lD l "SupD1y"tubeleading etanm'sto the burner; 4

The molteiior heat softened glassintr'oduced into the combustion chamber l8 is'deposited on the bottom wall 12 of the'burner and this well maybe shaped to provide a well 32 for accommodating the heatsoftenedglass. Referring again toFi'gure' l of the drawings,'it will be noted that the well is generally conicalin shape with the apex in axial alignment with the burner and with the inner surfaces tapering outwardly to the discharge slots l8in-the side wallof the burner.

The burner I0 is rotated. at a speed to provide thecentrifugal force required-to flow the molten or heat softened glass generally radially outwardly along the inner surface of the botom wall I2 to the discharge'slot's 28. It is importantto note 7 that as the molten or heat softened glass flows radially outwardly over the bottom wall 12 any cords that may be present in the glass are stretched and thereby reduced in size. Thus the molten glass is mixed to some extent as. it flows outwardly along the bottom wall l2 and'the homogenity of the glass is improved. Y I

The centrifugal force resulting from rotation of the burner I0 is also 'sufficient to actually project theheat softened glass through the discharge slots-.28 and into the blasts of burned gases issuing. from the discharge slots... .Ifdesired, the heat softened glass may .be separated into a mul-.- tiplicity of individual streamsof filaments by serrations 33 formed on the bottom edges of the discharge slots 28.. As a result. relatively small streams-of heat softened glass are projected into the blasts of burned gases discharging from the slots 28. This general arrangement provides in effect a two-phase attenuation of the heat softened glass, the first phase being accomplished by drawing outpthe "heat softened glass under the influence of centrifugal forcev and the second phase being accomplished by the force of the burnedgases contained within the blasts.

Any suitable means may be provided for rotating the. burner If] at the desired speed. .In the present instance a pulley 34is secured to the burner I0 adjacent the upper endof the latter and is'supportedon the support 15 through'th'e 'medium' of "thrust bearings 35. This pulley is connected to "a suitable prime mover, not shown herein. by a-belt 36. The speed at which the burner I0 is rotated depends upon the viscosity of the glass deposited on the bottom 7 wall l2 of the burner and also to someextent upon the size of-fibers required; Assuming for-the purpose of "the centrifugal force required to flow theheat softened glass radially outwardly into the blasts. It 'is' to be understood, however,;that thepartlcular speeds noted above arenot critical and may be varied considerably depending upon the viscosity of theglass deposited on the bottom wall I2 of the burner. r

' Operation n I In .use,.glass or materials having characteristics similar to glass is introduced into the chamber l6 of the tube l9 and isdeposited in the well formed by the bottom wall l2 of the burner. As the glass or other material .passes from the deliveryend of the supply tube l9 to-the well 32 it is heated by the burning gases within the combustion chamber I8 to a temperature sufiiciently high to melt, or substantially soften the glass or other material. During the .above operation the burner I; I0 is rotated :about ,the .vertical axis of the combustionchamberl 6 and the heat softened 6 material deposited on the innersurface of the well 32 flows; radially outwardly vunder theinfluence of centrifugal force. As the-heat softened material passes "over. the serrated surfaces; 33 l of the outlet slots 28 -itis divided into'amultiplicity of generally radially extending closely spaced;-

streams. Thesestreams are introdueeddireotly into the'burned'gasesor products of combustion flowing throughtheslots 28 so that the-force of the gases coact with thecentrifugalyforce acting on the heat -.softened material to draw out the streams and project :the. same into theblasts issuing from theslots 28. Thus regardless of the peripheral speed 0f..the slotted portion of; -the burner, vthelindividual streams-are projected ra dially outwardly into the blasts-and are further attenuated to form; extremely fine fibers by the heat and force, of theblasts- Referring now to the embodiment of the in vention shown in Figure 4 ofthe drawings, it will be noted that this construction differs from the apparatus previously described in two major re,- spects. :In the firstplace, the glass tank 29 is-replaced by means for feedingglass forming material such as glass cullet or glass marbles directly into the combustion chamber315of -,the burner 36.. In the second place, .theburnery3li .is fixed againstrotation with the exception, of the bottom wall 31 and the latter issupported for rotation about the vertical axis ofthe burner. a The means for introducingglass forming material such as batch, cullet or marbles into; the combustion chamber 35 comprises; a supply tube 38. similar to the ,tube l3 inthatthe lowerend projects into the upper. end of the combustion chamber 35 through the central opening formed in thering 2 l The upper endofthesupply tube 38. is connected to a source of supply, not shown. r the ss rm ater al. 1 Inasmuch as the combustible :mixture of gases in the chamber 35 burns underpressuressomewhat above atmospheric; it may be necessary; to provide a pressure look within the tube 38. A suitable pressure loci; is diagrammatically, shown in Figure 4'and may be similar to the. one disclosed in the Dockerty Patent2,286,903. In any case. the purpose of thepressure; loci;v is to prevent the burner chamber pressure'from escaping through the supply tube 38 whenglass forming material is fed tothe combustion chamber. In

general, the pressure lock comprises two slide valves 39 and .40 spaced from each other in the direction of length of the supply tube. 38 and operfable independently of one another. The arrangement is such that when it is desiredsto feedglass forming materialinto the-burner the top valve 39 is closed and the bottom valve 40 isopened yenabling the material trapped between the two valves to drop by? gravity into the combustion chamber 35. 1

As the glass forming material passes downwardly through the combustion chamber 35ft is heated to asufficie'ntly high temperaturefto form a body, of glass and the latter is deposited in the well 4| formed by bottom wall 31 r theburner. The bottom wall 31 is formed separately from the side walls ofthe burner and cooperates with the bottom edges of the side burner walls to form an annular outlet opening 42 through which the products of combustion or burned gases escape from thechamber, 1

, As in the first described form of the invention,

.the cross-sectional areaof theannular outlet opening. is so. proportionedywith respect to the volume 201' the combustion. "chamber. 35 that "are" thr6fl'gh tiie annular eemfie emme ram-er a 'eiire uke-imes't new i temeeretere exeee'eme the; softenin fie ure'efeleee ate nevifi 'evereeity eumeiente 1 V eat- S tne'd eflaissfinto peed determinedfitoprovide the htrireear tree 2 r qiiiree w flow l i'atisoftened m s e'e ierallyradtan v cutwafdiy alone the ne'r erfaqe' ot ttle wan: 31 to-the: rimmer: outlet teem-he 12. If j'deieiird, the te r ennmar iedg'e 43 f the lsettomwam- -31 fiiai be serratemterthe pi'ifieoteer eeper j tiethe =l reet' -softened;gla s til-to a mertipl iegty oi in'fivieeer.etreamebefore the g lase-ae aiseriarg'ee through the outlet o sem ing 42. As the he t sefterieer "glase haws but yifirdli over the -eeri'pheral e'qge of the bottom Waller trite the-ermine; outlet '42 itieeuhjecte'l to-th of-if the tcroee eaeee' eferoduecs "of eembuetiee e'eeiame mm the eomb-uetioneuem mi-"35. the heat sane-nee elass' i prawn throagh' tfi erminar benef t! '59 the meet" or he? e21eaes andi'eettemrated mto beiby th'e ii'eeteneroreeortnib1ast. V bbttoh i' wan "3:1 lie ro'tatea at the tleeired eeeeq beaten "at art 43 "treatediu bearrngs M in ee *eetpemea support 45. A pulley 46 m seeered tetne shaft between me beerlrree and is co etea to a smtameprime moverd1hyebe1t4a.-- e f Y 1 "e 'meeiheatiefi'tlmwn 'in Ffie flre or t e wifie' ilmstretes a bemer umt sim'nerte the the watered "in Figure 4' EYEept-that the bottom ner and the incomin cmb'il'tible mixture'ergases i5 ei r'eetea gfie'fally radiall inwardly toward the vertical axis ofthe burner. -A-l's0, molten ewes 1s supplier?! to the combustion eham'ber 50 from a tank-5| containing a heady of moltefrglas's m1 eeitably' suoportee "directly above the hur-hen meetail; the bottom wall 49 is eennecteeet its center te "the lower end :61 a'verticarshaftsz firmed er a high heat rei'staht -ma-terial, such for examele as nickel, tungsten: or platinum. Thi shaft projects upwardly threugh the combustlen chamber 50 and through the tank =51 to point tubs-teatime eteve the top wall of-this tank The either enter the shaft'is' jou-rnaled iii bearmee se and is eenneetea te -prime mover,

not nlhreih elicits onpass agesv formed; in the annular it. lrhe combustible mixture 1 or gases mews s7 throfighl'lthe annular; rin 51 under pr ur abotezatmospheric and assa consequence the-mol ten leaving.- the IQWQIEIld? of the cylinder lifi is directed inwardly against; the shaft 52 to wet thelatter; .'I-lit1s the molten glass flows downwardIy-"along the shaft -52 into the combustion chamber and :SUbjBCted to the hightemperatine bf the burnlnggaseswithinthis chambe The molten: glass, "eventually is "collected on the bottom: wall 49 ,and flows outwardly under the influence-" ot centrifugal force; into the; annular blafitrdischargi'ngefrom the circular outlet open-- the ".58; which. corresponds to the opening fez-hue? scribed in'comrectibn with'Eigure 'The operationv'ot the-embodiment shown 'in ,Fig;ureT5 is eenrallythesame as the operation previously elescr-ibedfin connection with'FigureA;

* wecl'aimz' f r. l-The process' of. making fibers from a heat softnable material which' comprises burning =9, combustible mixture of 'gaseswithin a s'ubstan tially closed chamberand discharging the burned "gases *generally outwardly and radially from the chamber invthe former a blast moving at a re- .loeity: sufiicient" to attenuate .the heat softened material into'fibrs, heating it body of theemae terial to :softened state Within said "chamber, subjectmga body ofsald heat' softened material to thexactioh of centrifugal force to flow theheat softened material into the blast, and entraim'ng the heat isoftenedmaterial in the blast whereby the material isrcarried :away from the chamber by the filast'and is attenuated into fibers by the lieatand force of the blast.

2; Thei roee'ss of'makirigfibers from a mate- 'ri'alcapable of being 'softenedxby heat which comprises burning a. eomb-usttlile. mixture'zif eases within a substantiall closed chamber' and disehare-ine the burned gasesfrom arestricted outlet in -''a Wall" of tHechamber in the forn'r-o'f a u sta' itially continuous, annular blast uniting atevelocity sufii'cient to attenuate heat softened material into fibemheating a body of themateri'al to a molten 's'tate withinsaid chamber, subjecting-the heat softened material to the iee- "tlonpr eentrirugel fer'ee to flew the heet sefteneq r -naterialunder the influence of the cemlf i al r e t d y i o the annular blast of the lournecl sgases discharged from. the chamber-whereby the. heat softened material carried away from the chamber by. the blast, and attenfiating. the -=heat=softened-materia1 into'filriers, .bythe hat and forceof the bl'aist. 1 v 3. 'I he proce'ssof making glass fibers which comprises burning a combustible mixture of gaseswithin fa substantially closed chamber and disc ar ng the turned easesflxreu h en aperimg ln one fsieeerthe chamber adjacent the bottom ell of 'th'fla tter in the "form of a radially mree-teablast of a temperature above-theattenuating temperature of glass and having 2. velocity suflicient to attenuate softened glass into fibers; heating albodyx'of glass to a temperature whichexcejedswm softening point of glass by -v-1ntroducingthe body of glass into the burning wgases within the "chammz r, collecting the heat wsoftenedvaglasson the bottom wall of the cham- 1 her" andeubgiectiiig the'he'at softened lassta the action-6f centrifugal-force "flowing the heat eonened eg lass under the influence or "centrifugal rforce ovei' the-bottom1'wal1' of 'theehambr in an outward-direction and mto the burned'igtises cise ergee "as/a met through 'thebfitlet epexi- ;mg: and v"entraining "the heat edftened glase ih 9 the blast'whereby the glass is attenuated into fibers by the heat and force of the blast.

4. The process of making glass fibers which comprises burning a combustible mixture of gases Within a substantially closed chamber and discharging the burned gases through an opening in one side of the chamber adjacent the bottom Wall of the latter in the form of a radially directed blast of a temperature above the attenuating temperature of glass and having a velocity sufiicient to attenuate softened glass into fibers, heating a body of glass to a temperature which exceeds the softening point of glass by introducing the body of glass into the burning gases within the chamber, collecting the heat softened glass on the bottom wall of the chamber and subjecting the heat softened glass to the action of centrifugal force, flowing the heat softened glass under the influence of centrifugal force over the bottom wall of the chamber in an outward direction into the outlet opening and into the burned gases discharged as a blast through said outlet opening, separating the heat softened glass into individual radially moving streams as the glass leaves the chamber, and entraining the streams of heat softened'glass in the blast whereby the glass is attenuated into fibers by the heat and force of the blast.

5. Apparatus for producing glass fibers comprising a vertical burner having a chamber within which a combustible mixture of gases is burned to provide a temperature within the chamber which exceeds the softenin temperature of glass, means for introducing into the chamber a body of glass which is heated by the burning gases in the chamber to a temperature above the softening point of the glass, a bottom wall for the chamber having the peripheral edge spaced below the sides of the chamber to provide an annular outlet opening so proportioned with respect to the volume of the combustion chamber that the burned gases are forced from if) through said outlet opening and into the blast of gases escaping from the chamber, and means at the peripheral edge of said bottom wall for separating the heat softened glass into a multiplicity of individual glass streams.

'7. Apparatus for producing glass fibers com-.

ature above the softening point of the-glass, a

bottom Wall for the chamber having the peripheral edge spaced below the sides of the chamber to provide an annular outlet opening so pro- I portioned with respect to the volume of the comthe chamber in the form of an annular blast I ward direction through said outlet opening and into the blast of ber. V

6. Apparatus for producing glass fibers comgases escaping from the champrising a burner having a chamber within which a combustible mixture of gases is burned to-provide a temperature within the chamber which exceeds the softening temperature of glass, means for introducing into the chamber a body of glass which is heated by the burning gases in the chamber to a temperature above the softening point of the glass, a bottom wall forthe chamber having the peripheral edge spaced .below the sides of the chamber to provide an annular outlet opening so proportioned with respect to the volume of the combustion chamber that the burned gases are forced from the chamber in the form of an annular blast having a temperature which exceeds the softening tem perature of the glass and having a velocity high enough to draw out the softened glass into fibers, means for rotating the bottom wall at a speed determined to provide the centrifugal force required to flow heat softened glass collected on the bottom wall in a radially outward direction bustion chamber that the burned gases are forced from the chamber in the form of an annular blast having a temperature which exceeds the softening temperature of the glass and having a velocity high enough to draw out the softened glass into fibers, said bottom wall being shaped to form a well for collecting the heat softened glass, andmeans for rotating the bottom Wall at a speed determined to provide the centrifugal force required to flow heat'softened glass in a radially outwardly direction over the bottom Wall 1agldtthrough the annular outlet opening into said I as.

8. The process of making fibers from a heat softenable material capable of being drawn out into fibers when in a softened state which comprises burning a combustible mixture of gases force into said blast, and entraining the material in the blast whereby the material is attenuated to fibers by the heat and force of the blast. 9. The process of making fibers from a heat softenable material which comprises burning a combustible mixture of gases in a substantially closed chamber and dischargin the burned gases from the chamber in the form of an annular radially directed blast moving at a velocity sufficient to attenuate the heat softened material into fibers, subjecting a body of said heat softened material to the action of centrifugal force to flow the material under the'influence of the centrifugal force into the blast whereby the material is conveyed from the chamber by the blast, and attenuating the softened material into fibers by the heat and force of the blast.

CHARLES J. STALEGO.

WENDELL W. DRUMMOND.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 

